1. Field of the Invention
The present invention relates to a DC rotary machine.
2. Description of the Prior Art
There is well known and widely used in the art a type of DC rotary machine comprising a first coil assembly for a motor and a second coil assembly for a generator rotating together. Such DC rotary machine is used, for example, as a rotary machine for tape recorder, VTR etc.
In use, the rotational speed of the DC rotary machine is kept constant by a speed detection and control apparatus. A DC signal representative of the rotational speed of the motor element is derived from the generator element and the DC signal is applied to, for instance, the speed detection and control apparatus. In response to the signal, the speed detection and control apparatus controls the supply of current to the motor element so as to keep the rotational speed of the DC rotary machine constant.
In almost all of the conventional DC rotary machines of the above-mentioned type, the output rotary shaft of the motor is coupled with the input rotary shaft of the generator so that the two shafts may rotate together as a unit. Such coupling between the two rotary shafts brings about a mechanical resonance by which some reduction in accuracy of the DC rotary machine may be caused.
DC rotary machines of the type pertinent to the present invention are also used in detecting, for instance, the rotational speed of a motor and controlling the speed. For this application of DC rotary machine, it is desired that a ripple wave in the wave form of the generated voltage from the generator be reduced to a minimum to attain a high accuracy of operation.